Radio beacon



Nov. 23, 194s. R, R. BRUNNER Re. 23,050

RADIO BEACON Original Filed March 2 1944 5 Sheets-Sheet 1 Pffa Beam/Mae, ofcfsfp,

BY il Nov. 23, 1948. R BRUNNER 4kRe. 23,050

RADio BEACON Original Filed March 2, 1944 5 Sheets-Sheet 2 f i v Kze,

5,7 MA1/ev M Eeuw/VER- Nov. 23, 1948. t R. R. BRUNNER n Re. 23,050

RADI O BEACON original Filed Marh 2, 1944 A 5 sheets-sheet 4 for l!! NW L u Nov. 23, 1948. R. R. BRUNNER Re. 23,050

RADIO BEACON original Filed Maron 2, 1944 5 sheets-sheet 5 vlas eissued Nov. 23, 1948 Re. l23,050

RADIO BEACON Reed R. Brunner, deceased, late oi Baltimore,

Md., by Seismograpb Service Corporation Tulsa, Okla., a corporation oi' Delaware, as-

signee original No. 2,417,8ov, dated Mai-h 25, 1.947, serm No. 524,122, Mai-cn 2. 1944. application for reissue February 25, 1948, Serial No. 10,822

(Original granted under the act of March 3, 1883,

15 Claims,

The invention described herein may be manufactured and used by or for the Government of the United States or for governmental purposes only without the payment of any royalty thereon.

This vinvention relates to radio beacons and more particularly to radio beacons affording a number of optional approach paths which may be selected by the operator ci the 'guided vehicle.

There are available at the present time three general forms of radio bacon for -guidingairborne vehicles on predetermined paths in space. In one of these forms, `there are present a plurality of directive radiation lobes. either modu-v lated or keyed with interlocking signals, and oncourse indications are secured in the plane which is the locus of all points of equal intensity of the adjacent lobes. In this type of beacon, the number of approach paths is determined by the original design of the beacon installation, and varies in the systems so far disclosed from two to twelve, with the four course beacon at present the most common. 'I'he course definition is about plus or minus two miles laterally at one hundred miles. In a second form of contemporary beacon, there is employed a rotating directive lobe of radiant energy, withusome means for vindicating the passage of the' radiation maximum through a predetermined direction.l The signal at the mobile vehicle is then applied to some form of phase indicating apparatus to perform the bearing finding operation. Here again, accuracy is of the order of plus or minus one degree giving a lateral course definition of plus or minus two miles at a radial distance of one hundred miles. With this beacon, the bearing from the beacon may be determined, whatever the location of the vehicle with respect thereto, and it is frequently referred to as the omnidirectional beacon.

. Of late there has been described a beacon in which frequency modulated energy is applied to a pair of spaced radiators, and since the relative time displacement of the two energies arrivingat a mobile vehicle in the iields of said radiators is a function of its angular position with respect to a line passing through the radiators. beat frequencies are derived in apparatus carried on the vehicle which are indicative of the bearing of" portiony of the frequency spectrum, and satisfacas amended April 30, 1928; 370 0. G. 757) tory operation is obtained only when two or more cycles at the beat frequency occur during carrier excursion in any one direction. Further, at each reversal of the frequency sweep there is disturbance of the input to the indicating instruments, and at some angles, complete cancellation oi the energy between the positive and negative' sweeps occurs. Here again, lateral-course definition-at a distance of one hundred miles is approximately plus or minus two miles.

One of the principal objects of this invention i is to provide anew and novel radio beacon system having improved lateral course definition.

Another object of the .invention is to provide an improved omnidirectional radio beacon.

Still another object of the invention is to prov rived from the first mentioned energies is employed to actuate one' element of a phase indicator, while a stimulus derived from the last mentioned energy is impressed on the other element thereof. The phase meter serves to indicate the angular direction to the vehicle from 'a reference line through the radiating system.

Other objects and advantages of the invention will in part be disclosed and in part be obvious when the following specication is read in conjunction with the drawings in which Figure 1 is a block diagram illustrating the essential features of the invention.

Figure 2 is a diagram illustrating the method of computing the difference in path length with the mobile vehicle remote from the beacon location.

Figures 3, 4, and 5 are diagrams showing the loci of points at which the reference phase meter reading is obtained.

Figure 6 is a Iblock diagram showing' an alternative method of practicing the invention.

Figure 'l is a.` detailed schematic diagram of transmitting apparatus for exciting the beacon antenna system.

Figure 8 is a detailed schematic diagram of receiving apparatus for translating the received mit and the output in lead 24 from 3 energy at the mobile vehicle in to bearing indications.

In the description of the structure and oper-` ation of the invention the adoption of a mathematical notation for the presentation is convenient.

n is an integer expressing the harmonic order.

w=2r times a second carrier frequency, differ-V ing from the first carrier frequency. p is the phase meter indication. 9 is thev azimuthal bearing angle of the from the transmitter.

Referring now to Figure 1, the beacon transmitting apparatus indicated generally at I inreceiver cludes antennasV II and I2 spaced by a distance 3 2a. The radio transmitter I l having an output voltage E=A sin wt is connected to and energizes radiator II, and radio transmitter Il having an output voltage E=B sin (w-I-mt is connected to and energizes radiator I2. Located in the common radiation field of antennas Il and I2 is the antenna 12 connected to a demodulator and ampliiier 13, of any suitable type, having the output thereof impressed on the modulating stage I5. The modulating stage I5 also receives energy from the radio frequency oscillator I6 and the co-actlon of the output from oscillator i6 and demodulator and amplier I3 in modulator stage I5 produces an output voltage E=C(1|M cos Slt) (sin p't) whichoutput is impressed on an antenna I I which may be centrally disposed between antennas IIl and I2. As is apparent from the equations, stage I5 produces amplitude modulation at a frequency equal to the diilerence between the frequencies of transmitters I 3 and I4 but if desired the energy impressed on antenna I1.could as well'be frequency modulated. The function of the apparatus connected to the central antenna I1 is merely to radiate reference energy at a frequency il and this function is equally well iuliilled bythe employment of phase, amplitude, or frequency modulation, or other known systems for producing in a remotely located radio -receiver energy at a frequency n. The mobile vehicle whose angular bearing is to be determined w is-located at I8 and includes antennas I9 and 2II connected to the receivers 2l and 22Vtuned re spectively to w' and u. The resulting output in the lead 23 from receiver 2i has the form cosine receiver '22 has the form cosine between antenna II and the receiving location it. and antenna i2 and the receiving location It respectively.

inspection of the expressions for the voltage in leads 2.4 and 23 shows that the phasemeter ina dication will be constant so long as the vehicle carrying the receiver moves in a manner maintaining the quantity (di-dz) constant, as the factors n and A are constants determined'by the design of the installation. "n refers to the harl@ manic order of the modulating the radiation from antenna I1, and

where c is the velocity oi' propagation of electromagnetic waves. As the curves of constant phase meter indication are the loci of constant difference in the length of radii to two foci, it is clear that their plane projections have the form 2; of hyperbolas. When this system is used for the guidance of airborne craft, it is found that the ioci of points of constant phase meter indication are the surfaces of hyperboloids Vof revolution. In the balance of this presentation, consideration will be limited to the case in which separation of the vehicle from the beacon system exceeds ten times the spacing oi antennas Il and i2 and the eiect of departure from the ground plane under these antennas is negligible.` For these conditions, the approximations of Figure 2 suice for the determination of the phase relations between the two alternating currents applied to the phase meter 25. i

In considering the operation yof the apparatus of Figure 1, with n=1, let it be assumed that the mobile vehicle is remote from the beacon and that it is displaced to the right of the perpendicular bisector of the line dened by the antennas II and I 2. The distance di is therefore greater than 40 dz and the approximations of Figure 2 are valid. Energy arriving at Il from antenna II requires a certain time for transmission, and the resulting voltage may be represented by el-G sin u( L The energy from antenna I2 requires a lesser time for transmission and arrives with a voltage d. ca wd. COB (wt--Ql-T c (M+T) which is, in simplied form I w Qd, cos [Qt-I-Ml-dz) -l These forms result from the combination of the two signals in accordance with the cosine law and the derivation ofthe envelope equation for the voltage wave produced.-v They correspond to the voltage wave on lead 24.

Antenna 12 is shown located on the pei-pendio ular bisector of the line joining antennas II and 7.0 I2, thereby making (d1-dz) at this point. As

will-be shown later, in practice the error introduced by the term energy aiecting sacco does not amount to more than 0.1 degree and may be neglected. The envelope of the output from modulating stage Il therefore has the equation Moos ntattheantenna II and arrives atthe receiving'location il with the form cos Here d has a value intermediate di and d: and i may be representadas dira. The form given is that of the voltage wave on lead 23.

The angle indicated by the phase meter 2i, which-may be of any well known type, is the difference in phase between the input from receivers 2| and 22.

Qi-dz) very nearly Elimination of the last term is permissible.' since il will usually correspond to a frequency of 1000 c. p. s.. and 6 cannot exceed a in Figures 1 or 2. If a be taken as 100 meters, evaluation of the term shows it to have a maximum value of 0.002 radians or 0.1 degree, which as above noted. need not be considered.

From Figure 2, (d1-dz) =2a sin o. Assuming that the frequency of the currents applied to the phasemeter 2i is multiplied by n, the nal expression for the phase meter indication is 36011.24 sin degrees. Conning attention to the course dennition in the immediate vicinity of the perpendicular bisector of the line joining the antennas I I and I2, and calling the distance from the base of this line to the vehicle d, sin a may be taken as where srepresents the lateral deviation from' the reference course line. Then. letting a=57\ and Taking 0.01Y radians, or 1.8 degrees as an easily discernible phase meter reading, the corresponding course definition is:

Thereiore, if d be 100 miles, s=4264 feet. far surpassing the locating accuracy of any contempo- ,rary system. Employing a multiplication factor another and will appear as a zero indication. As

shown in Figure 3, there is but a single path 2l along which phase meter zero indications are obtained when the spacing of antennas I I and I2 is less than a full wavelength. Figure 4 shows the two course lines 21, 28 along which zero phase meter indications are secured with an antenna spacing of one wavelength, and Figure 5 shows the twenty course lines along which zero phase meter indications are secured with an antenna spacing of ten wavelengths. The invention is most conveniently practiced in the very high frequency portion of the. radio spectrum since, for example, an antenna spacing of ten wavelengths with a radiated frequency of 100 megacycles per second is 30 meters or about 100 feet.

The positional ambiguities resulting from the employment of a system having the characteristics of Figure 5 to secure great accuracy may be resolved by the use of a system having the characteristics of Figure 4 with the fundamental frequencies impressed on a ilrst phase meter, and at the same time multiplying the frequencies at the receiver and impressing the energy thus derived on a second phase meter to provide sensitive indications; Then, when the sensitive phase meter shows a zero indication, it may be readily determined by consulting the fundamentally excited phase meter whether the craft is on the zero order, first order, second order, etc., course line of constant phase meter reading.

A disadvantage ofthe system of Figure 1v is the fact that two carrier frequencies are employed. The system of Figure 6 makes more eflicient use of the available spectrum space. Here, the radio frequency voscillator 29 having the frequency w energizes the antenna il through the modulator 30. The antenna I2, spaced from antenna II by the distance 2a is energized from the radio transmitter II having the output frequency w-Hz, and

the antenna l2 is excited from thecommon iields of the two antenna systems. Voltages from the antenna l2 are'impressed on the demodulator 32,

whose output is passed through the filter 33 tuned to the difference frequency between the alternating current energies supplied to antennas II and I2. The output from filter 3l is then fed to the frequency multiplier 3l whose output controls the emanations from antenna II through the modulator 30. Passage of Athe energy from iilter 33 through the multiplier 34 increases the frequency thereof by the factor 11. Upon intercepting and demodulating the signal received at the mobile vehicle from the radiating system described above, there are obtained in the demoduiator output at the vehicle a current of the form cos n n, whose phase is independent of the bearing of the vehicle from the beacon, and a current of the form cos The two currents are separated by lters at the receiver, and the rst is applied directly to one e5 of the operating windings of a phase meter, while the other is passed through a multiplier corresponding to multiplier 34 and then impressed on the other operating winding of the phase meter. The indications obtained are substantially the same as those secured with the system of Figure' 1 and the operation of the apparatus is fundamentally the same. A detailed description of apparatus suitable for use in the arrangement of Figure 6 will now Foe given.

The equipment presented in Figure 'a' includes all the apparatus situated at the beacon location. in this and the remaining figure, heater circuits for the vacuum tubes are merely indicated as the nnal configuration thereof may be varied at will by the designer. Antennas |2 and 12 are stationary and are associated with each other in the spacial relationship indicated in the previous figures. The position-oi antenna 112 may be made adjustable if it is desired to control the position of the course lines of zero phase meter indication.

The piezo-electric crystal 35 is connected betweenl the control grid 36 of the vacuum tube 31' and ground in shunt with a resistor 38. The cathode S9 of the tube 31 is directly connected to ground,

'and the anode 48 receives energy from a positive ,tap on the anode source 4| through the parallel circuit of inductance 42 and capacitance 43.

With the resonance frequency of the circuit 42, 43 set slightly above the resonance frequency oiv the crystal 35, oscillations are set up at a frequency controlled by the constants of the crystal 35 and its holder, and the oscillation energy is applied to the control grid 45 of the power amplifier tube 46 through the coupling capacitor 44. A choke 41 and grid leak resistor 48 are connected between the grid 45 and ground to provide a part of the operating bias, the balance vof vwhich is secured from the voltage drop across the resistor 49 connected between the cathode 5| and ground in shunt with the bypass capacitor 58. The anode 52 of power amplifier 46 is energized from the high voltage positive terminal of anode source 4| through the parallel resonant circuit formed by the Vcapacitor 53 and the primary-54 of the ondary 56 connected between the radiating antenna II and ground. The space charge grid 51 grounded for radio frequency currents by the capacitor G8.

, A second piezo-electric crystal 88 differing in frequency from crystal by an amount represented by Q in the previous portions of the presentation is connected between the control grid 8| of the oscillator tube 82 and ground in shunt with a grid leak resistor 83. The cathode 84 of the tube 82 is connected directly to ground, and thus to the negative terminal of the anode source 4| which is also grounded, and the anode 85 is excited from the positive tap on source 4| through the inductance 86 shunted by adjustable capacitor 81. As is Well known, the adjustment of the circuit 86, 81 to a resonance frequency slightly above the crystal resonance induces oscillations in the circuit at a frequencycontrolled by the Vresonance frequency of the crystal` 88 and the shunt capacity across said crystal. The alternating current component of the voltage at anode 85 is impressed on the control grid 88 of the power, amplifier tube 89 via the blocking capacitor 98, and the return for grid 88 is provided by the radio frequency choke 9| and grid resistor 92 connected in shunt therewith to ground. As before, bias for the control grid 88 is provided in,

minal of said source 4| through the primary 98 of the output coupling transformer 99 whose secondary winding |88 is connected between' an; tenna l2 and ground. Primary winding 88 is shunted by 'the adjustable capacitor |8I, which is adjusted as customary, for minimum direct current in the output circuit of the vacuum tube 88. v

The two oscillator and power amplier combinations so far described anord means for en ergizing the antennas if and |2 at radio frequencies diiferingfrom one another by the amount Q, and differ primarily in that position is made for the modulation of the energy derived from oscillator tube 3l. The antenna 12 responds to the radiations at each of the frequencies, Which are sufficiently closely spaced that a resonant circuit of ordinarily encountered Q is responsive to both. The voltages at antenna 12 are impressed on the primary winding |82 of the input transformer |83, and the secondary |84 thereof is connected to the control grid of the biased detector tube |88 in shunt with the resonating capacitor |81. The cathode |88 of the tubei 86 is connected to ground through the series circuit of inductance |89 and capacitanceV ||8 resonant to alternating current of frequencyn. A direct current path to ground from cathode |88 is provided by the bias resistor connected therefrom to ground. The space charge grid ||2 is connected to the intermediate tap on source 4| through the dropping resistor I|3 and grounded for alternating current energy by the connection of bypass capacitor H4 from the grid ||2 to the cathode |88.

The anode ||5 of tube |88 is supplied fromthe intermediate voltage tap ofthe source 4| through the primary IIS of the transformer H1 and the primary H6 is shunted by the capacitor I8 having a value selected to resonate with the inductance H8 at the frequency Q which is the diifer= 'ence frequency between the alternating currents iny antennas Il and |2. A. filtered alternating voltage at frequency n appears across the secondary I|9 of transformer IVI1 and is symmetrically impressed on the control grids |28, |2| of the frequency multiplier tubes |22, |23 through the current limiting resistors |24; |25. Operating bias for the control grids |28, |2| is provided by the connection of the cathodes |25 and |21 to ground through the biasing resistor |28 shunted by the capacitor |29. The values of the bias resistor |28 kand the limiting resistors |24 and |25 are selected to provide a maximum of output at the third harmonic of the input 'frequency. The anodes |38, |3| ofthe frequency multiplier tubes are connected respectively to which then appears in the secondary winding |35 connected between the control grid |38 of the amplifier tube |31 and ground.V As in previous stages, operating bias for tube |31.is supplied by the connection of the cathode |38 to ground through the bias resistor |39 shunted by the by:- pass capacitor |48, and the suppressorgrid |4| is also connected to the cathode |38 to provide pentode operation. Excitation for the space charge grid |42 vis secured from the source 4| through the dropping resistorY |43 whose grid end A is connected to ground througha capacitor |44', and the anode |45 is connected to the same source the suppressor grid 84 internally connected to' the cathode 85 returned to ground through the bias resistor I8 and shunting capacitor 81. The anode 88 of this modulator tube 63 is connected to the space charge grid 89 ythrough the primary winding 10 of the transformer 58 and this point is then returned to the intermediate positive terminal of the source 4|.

The apparatus thus far delineated corresponds to that situated at the beacon location in Figure 6, and its operation is substantially 'as follows:

The oscillator 82 and po'wer amplifier 88 are adjusted in the usual `manner by setting the capacitor 8 1 to a valueresonating the anode circuit of crystal oscillator 82 to a frequency somewhat higher than that of crystal 80 and adjusting thel variable-capacitor in the anode circuit of tube 88 for minimum anode current. Antenna I2 is then excited with a voltage wave whose form may be taken as sin (v+m t. With the receiver connected to antenna 12 temporarily de-energized. the oscillator 31 and power amplifier 4.8l

are similarly adjusted and excite the antenna with the voltage wave of the form sin wt. However, theexcitation for the space charge grid 51 in power amplifier 48 is subject to variation in accordance with potentials appearing in the sec- .ondary 58 of the modulation transformer 58, so

that when the receiver connected to antenna 12 is energized.l there appears in the anode circuit of the tube |05 energy at the difference frequency between the inputs to antennas I'I and I2, which is then multiplied in frequency in the tubes |22. |23 with the associated transformer |33 and filtered by the action of tube. |31 in conjunction with the tuned transformer |41 to vary the energy input to antenna at the third harmonic frequency of the difference between the frequencies impressed on antenna 12. As a result, the final form of the excitation for the antenna is (1+M sin 3m) sin it where, M, as usual, is a constant indicating the percentage of modulation. In practice itis desirable to keep the ratio of carrier signal intensities from antennas Il and I2 at four-to-one or greater and to limit the percentage of modulation to avoid the production so far described incorporates no provision forV maintaining this difference frequency constant. This function may be performed by the apparatus situated within the dashed enclosure |49 of Figure '1 in which the control grid |50 of the variable reactor tube i5! is connected to the ungrounded terminal of the crystal 80 through the blocking capacitor |52, the phase shifting resistor |53, and the phase shifting capacitor |54. The anode |55 of the reactor tube |5| is also connected to the crystal 80. through the capacitor |55 having negligible reactance at the operating radio frequency, and excited from the intermediate voltage tap on source 4| through the choke |51, while the space charge grid |58 is also connected to this point o! the source through the dropping resistor v|88 grounded at the grid end by the capacitor |80. The reactor tube |5| may be of the pentode type having the suppressor grid lil connected to the cathode |82 which is returned to ground through the biasing resistor |63 bypassed by capacitor |84. The control potentials for the reactor tube Ill' are obtained from the output of the amplifier tube |65 whose control grid |88 is connected to one terminal of the secondary I i8 of the transformer ||1, and the anode |81 of which is connected to the anode supply bus 1| through the primary |88 of transformer |89. As is the custom, operating bias is provided by connecting the cathode |10 to ground through the resistor |1| and parallel capacitor |12.

The amplified currents in the secondary |13 of transformer |88 are passed through the divided circuit comprising the primary winding |14 of transformer |15 and the series combination of capacitor |18 and primary winding |11 of transformer |18. The current flowing in the winding |14 is substantially in quadrature with the voltage delivered by the secondary |13, and the value of capacitor |18 isselected to series resonate with the primary |11 at the intended difference fre- `phase changes bya change in output voltage.

This is done by connecting one termina1 of the secondary winding |88 .to the center tan of winding |19 whose extremities are connected'to the anpdes |8|, |82 of the rectifier tubes |83. |84 havinit. the cathodes |85 and |88 connected to either -end of the series connected resistors |81 and |88. Each of these resistors I 81, |88 is shunted by a bypass capacitor |89. |90, and the common terminal of the two resistbrs attached to the other end of the winding |80. The combination serves as a. discriminator circuit in which eoual and opposite polarities appear across the resistors |81 and |88 so long as the input fre'ouency remains at the assigned value. In the event of chance in frequency. the vector sum of the voltages in one branch of the rectifier circuit increases while the other decreases due to the change in the phase relations of the component vectors so that a net voltage is produced across the resistor combination whose slim is dependent on the direction of frequency deviation and whose magnitude is controlled` by the amount of freouencv deviation. This potential is employed as the control voltage for the variable reactor tube |5| by the grounding of cathode |85 and the connection of cathode |86 to the control grid |50 through the filter resistors |9| land |92. whose junction is connected to ground through the filter capacitor |83. .A lagging current is drawn from the circuit including crystal by the reactor tube |5| and this current opposes the effect of the crystal electrodes and other circuit capacitances. A positive voltage output from the circuit of the rectiers |83, |84 increases the amount of lagging current drawn and effectively decreases the capacity shunting the crystal 80, thereby increasing the oscillating fre- Il' quency. Since the normal operating frequency of crystal 49 is higher than that of eystal 95, this results in an increase in beat frequency, and as a result, the polarity of connection of transformers and |19 is chosen to provide a positive discriminator output voltage should the impressed frequency fall below the assigned value. Consequently. the discriminator circuit andassociated reactor tube act as a stabilizer returning the beat frequency between the outputs impressed on antennas and |2 to its preassigned value should anything cause it to vary. Positive beat frequency deviations produce stabilization in the inverse of the manner just described. The

complete combination of apparatus in Figure 7 radiates an unmodulated carrier from the antenna I2, and a modulated carrier at antenna modulated at the third harmonic of the difference frequency between the carrier frequencies ,on the two antennas, the frequency of the carrier on antenna i2 being adjusted by the apparatus in the enclosure |49 to maintain a constant difference frequency.

The composite signal thus produced is received on the apparatus of Figure 8, which may be located as shown at |94 Vin Figure 6. The antenna |95 intercepts and delivers the composite signal to the selective amplier and detector |96 in whose output there appear signals at the difference frequency due to the beat note between the two carriers and at the third harmonic of the dierence frequency due to the detection of the amplitude modulation on the carrier from antenna These signals are applied to the dividing networks including the capacitor |91 which is series resonant with the primary winding |99 of transformer |99 at the dierence frequency, and the capacitor 200 which is series resonant with the primary winding of transformer 202 at the third harmonic of the difference frequency.

The difference frequency output in the secondary 209 of transformer |99 is applied to the control grid 204 of the ampliiier tube 205 having its anode 206 connected to the positive terminal of the. anode source 201 through the transformer primary 209 of transformer 209 which is shunted rby the capacitor 2|0 rendering the circuit resonant to the difference frequency. The direct current circuit for the excitation of the tube 205 is completed by the connection of the negative terminal of the anode source 201 to ground and the attachment of the cathode 2|| to the same point through the resistor 2|2 and shunting capacitor 2|9, the latter combination serving to provide operating bias for the amplifier stage. The filtered difference frequency output appearing in the center tapped secondary winding 2| 4 of transformer 209 is symmetrically applied to the control grids 2|5 and 2|6 of the dual amplier tube 2|1 though the limiting resistors 2|8 and 2 I9 respectively. The limiting action of the resistors 2| 9 -and 2|9, combined with high negative grid bias secured by the connection of the cathodes 220 energizev the ano'de circuits of the tube 2|1. The

12 secondary winding 229 delivers energy at the third harmonic of the beat frequency to the rotatable winding 299 of the phase meter 25 from the output circuit of the tube 2|1. l

Energization for the remainder of the phase meter windings is vobtained from the train of ampliners receiving signal energy at the third harmonic of the dierence or beat frequency from 'the secondary winding 29|, of transformer 202.

One terminal of the winding 29| is' connected to ground and theother is attached to the control grid 292 of theampliner 299 having the anode 234 thereof connected to the positive terminal of source 201 through the primary winding 29S of transformer 299, this winding being tuned to resonance at the third harmonic of the difference frequency by the shunting capacitor 291. As in the previous stages described, bias is secured by the connection of the resistor 299 in parallel with capacitor 299 between the cathode 240 and ground. The output from secondary winding 24| of the transformer 236 is then applied to a phase splitting circuit; includingV a capacitor 242 and resistor 242 connected in series acrossxthe terminals thereofl and a second combination of resistor 244 and capacitor 245 connected in inverse order parallel therewith. By making the impedance of each of the Vfour circuit elements equal, there are secured across resistor 249 and capacitor 245, respectively, alternating current voltages of equal magnitude which are in phase quadrature with each other. Each of there voltages is impressed on a separate amplifier andcomblned in the well known manner of the Scott transformer connection to provide three-phase excitation voltage for the xed -windings of the phase` meter 25. y

Amplifier 249 has its grid 241 connected to the junction of resistor 249 `and capacitor 242 and its anode 25| connected to one end of the primary winding 249 of the coupling -transformer 249 tuned to the third harmonic of the. differ` ence frequency by the shunting 'capacitor 250.

' The other end of the primary winding 248` is nection of the control grid 258 to the junction point between the resistor 244 and capacitor 245,

providing an alternating current component passing from anode 259 through the primary winding 260 of transformer 26| and the source 201. The eiiiciency of this stage is increased by tuning the primary 260 to resonance at the third harmonic of the normal diiference frequency with the parallel capacitor 262. 'nie amplier 251 is also a pentode having the space charge grid 253 connected to the positive terminal of source 201 and thesuppressor grid 264 connected internally to the cathode 265 attached to groundby the parallel combination of resistance 266 and capacitor 261.

The secondary 266 of transformer 26| has inducedtherein a voltage which is in quadrature with that appearing in the center tapped secondary Winding 269 of transformer 249.` The relative gain of the amplifiers 246 and '251 is adjusted to make the voltage inthe winding 269 0.866 times the voltage in winding 269 and one terminal of winding 269 is connected to the .tween the currents fed to winding 22| and those fed to the three delta connected phase meter windings. A pointer 212 is linked to the frame carrying the winding 220 by tlie shait-`214 and provides a numerical indication of the phase angle by rotation over the-adjacent scale 215 which may be calibrated in degrees.

The apparatus of Figure a is carried on the mobile vehicle and responds to the radiations from the antennas Il and i2 of Figure '1 in the following manner."neglecting the eifect of terms which cancel in the final result:

Two.alternating currents of diii'erent frequencies are produced in .the amplii'ier and detector Ill, one having the form cos 3m, and the other having the form l cos (i'li- Fwd) or. optionally, I

cos-(nt the -iirst of which. it is seen. corresponds to the output from receiver 2| in Figure 1 with a multiplying factor of three substituted for "11." This is necessitated by the presence of the frequency tripler in the apparatus of Figure '7, which impresses amplitude modulation at the third harmonic of the difference frequency on the carrier radiated from antenna Il. The second current is seen to have a frequency equal to the beat frequency and to have a phase angle which isa function of the bearing of the mobile vehicle carrying the apparatus of Figure 8 from the radio beacon location. The current of` form cos 3m! is selected in transformer 202, amplified in ampliers 223, 2 and 281, split in phase and recombined to provide a three phase reference source for the excitationof the phase meter 2U. At the same time, the current-of form une) is selectedin transformer l. amplified in tube trebled in frequency in the multiplier tube 2i1 and applied to the rotor winding 230 ofthe phase meter 2i. The current applied to the rotor winding 220 thus has the form which is seen to correspond to the current in the lead 2l of Figure 1 with a multiplying factor of three substituted for "n. The phase meter inputs with this system are thus seen to correspond precisely to those obtained in the apparatus of Figure l. while the spectrum space required has been materially reduced by the elimination of the carrier frequency radiated from theantenna I1 in Figure 1. The visible operation of the phase meter is the same in either system and the 4same mathematical ex.

pressions give the relations between the bearing of the receiving apparatus-trom the beacon and sacco 14 the readings obtained on the phase meter. A total antenna spacing of ten wavelengths. :in conjunction with the above mentioned'multilplication factor of three lprovides a course .dei'i-V Anition of plus or minusas feet at 100 miles. in accordance with the earlier derived gures.

For the purposes of simplification in the ex- Vpianationof the invention, the residual phase shift terms possibly introduced by some of the components'. as by the leakage inductance of the transformers. have been neglected, as it is well known to introduce phase correctors in the apparatus for the elimination of such effects. Further, if it be desired to exert ilne control over the positioning of the space pattern of zero phase indication lines, not only may the position of antenna 12 be made adjustable as previously mentioned. but this may also be accomplished without the movement of antenna '12,V which may prove to be inconvenient by the introduction of a phase shifter between the demodulatorand am pliiier Il and modulating stage I! iny Figure 1, or between the demodulator I2 and filter u of Figure 6. It will be obvious that many changes and modi# ilcations may be made in the invention without departing from the spirit thereof as expressed in the foregoing description and in the appended claims. x

What is claimed is: 1. In a radio'beacon system, means for radiating wave energies of different frequencies from a plurality of spaced radiators. said energies'differlng in frequency by a Apx'edetermined frequency, and means jointly responsive to said radiated wave energies for radiating wave energy modulated by a harmonic of said difference frequency. y 2. In a radio beacon system, an antenna. a source of electrical energy having a predeterl mined frequency connectedto said antenna, a secondantenna spaced from said first antenna. a source oi' electrical energy having another predetermined frequency connected to said second antenna,y and means for modulating the energy of said second source in response to electrical energy having a frequency substantially equal to the difference between said ilrst mentioned frequency and said second mentioned frequency.

3. In a radio beacon system, an antenna, a source of electrical energy having a. predetermined frequency connected to said antenna, a

second antenna spaced from said ilrst antenna, a source of electrical energy having another predetermined frequencyv connected to said second antenna, means jointly responsive to the radiation from said antennae forderiving beat frey quency energy, and means responsive to said beatV frequency energy for modulating the energy vof 5. In a radio beacon system. an antenna, a.

source of electrical energy having a predetermined frequency connected to said antenna. a second antenna spaced from said first antenna,

a source of electrical energy having another predetermined frequelicy connected to said second antenna. means jointly responsive to energy from said sources for deriving beat frequency energy, and means for modulating the energy of said 16 orgy connected to said third antenna, and means for modulating the energy of one of said sources at a harmonic of said beat frequency;

second `source at a harmonic of said beat frel.

quency.

6.j In a radio beacon system, an antenna. s.

source of periodic ,electrical energy wnnected to said antenna. a second antenna spaced from said first antenna. a second source of periodic electrical energy connected to said second antenna,

and means jointly responsive to the radiation of said -antennas'for' maintaining aV substantially constant difference between the frequencies of said sources.

'Lin a radio beacon system, an antenna'. a-

source of periodic electrical energy connected to said antenna, a second antenna spaced from said first antenna, a second source of periodic elec'- trical energy connected to said second antenna, means jointly responsive to the radiation of said antennas for maintaining a substantially constant difference between the frequencies of said sources, and means for modulating one of sai sources at said difference frequency 8. In a radio beacon system, an antenna, a source of periodic electrical energy connected to said antenna, a second antenna spaced from said first antenna. a second `source of periodic electrical energy connected to` -said second antenna,

12. In a radio position determining system, an antenna. a source of electrical energy having a predetermined frequency connected to said an.

tenna, a second antenna spaced from said first antenna, a source of electrical energy having another predetermined frequency connected to said second antenna, and means for modulating the energy radiatedfrom one of said antennas in response to electrical energy having a frequency substantially equal to the dinerence between said ilrst mentioned frequency and said second mentioned frequency.

13. In a radio position determining system, an antenna, a source of electrical energy having a predetermined frequency connected to said antenna. a second antennal spaced from said first antenna, a sourcevof electrical energy having another predetermined frequency connected to said second antenna, means jointly responsive to the radiation from said antennas for deriving beat frequency energy, and means responsive to said beat frequency energy for modulating the energy radiated from one of said antennas.

14. In a radio position determining system, an

l antenna. a source of electrical energy having a means jointly responsive to the radiations of said first antenna, a second -source of periodic electricai energy connected to said second antenna, means jointly responsive to the radiations of said antennae for deriving beat frequency energy means responsive to said beat frequency energy for maintaining a substantially constant difference between the frequencies ofsaid sources, and means for modulating the energy of one of said sources at a harmonic of said beat frequency.

10. In a radio beacon system, an antenna, a source ofperiodic electrical energy connected to .said antenna, a second antenna spaced from said first antenna. a second source of periodic electrical energy connected to said second antenna,

a third antenna located on the perpendicular'bisector of a line passing through said first and second antennas in the radiation fields ofA said antennas, means for deriving beat frequency energy connected to said third antenna, and means responsive to said beat frequency energy for modulating the energy of one of said sources.

il. In a radio beacon system. an antennapfa source of'periodic electrical energy connected to said antenna, a-second antenna spaced from said first antenna, a second source of perioric electrical energy connected to said second antenna, a third antenna located on the perpendicular bisector of a line passing through said first and second antennas in the radiation fields of said antennas, means for deriving beat frequency enpredetermined frequency connected to said antenna, a second antenna spaced from said first antenna, a source of electrical energy having an-` ,other predetermined frequency connected to said second antenna, means jointly responsive to energy from said sources for deriving beat frequency-energy, and means responsive to said beat frequency energy for modulating the energy radiated from one of said antennas.

15. In a radio position determining system, an antenna, a transmitter for delivering electrical energy to said antenna, a second antenna spaced delivering electrical energy to said second antenna, said transmitters respectively including wave signal generators having different output frequencies, means jointly responsive to waves derived from said generators for developing a beat frequency signal having a frequency equaling the difference between said output frequencies and means responsive to said beat frequency signal for modulating the energy radiated from one of said antennas.

SEIBMOGRAPH SERVICE CORPORATION. Assignee of Mary M. Brunner, Administratris: of Estate of Reed R. Brunner,

Deceased,

By JAMES E. HAWKINS. v

' Vice President.

aEFEnENcl-:s crrsn The following references are of record in the file of this patent:

UNITED STATES PATENTS Earp Feb. 5, 1946 from said first antenna, a second transmitter for 

